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Plants defend themselves with armor made of sand

Thorns, poisons, and partnerships with biting insects are just a few of the ways that plants avoid getting eaten. Now, researchers have added one more to the list: armor made of sand. Scientists have long wondered why some plants secrete sticky substances that trap sand on their stems and leaves. Over the years, they’ve floated ideas from temperature regulation to storm protection to armor against hungry herbivores. To find out which is right, researchers removed sand grains from armor-wielding sand verbenas in California. After 2 months, the “naked” plants had twice the chewing damage of plants that kept their sandy armor intact, the team reports this week in Ecology. The study also shows that herbivores were far less likely to chomp off the flowers of honey-scented pincushion plants (pictured) when the researchers sprinkled some extra grains on the flowers. The key may be animal tooth care—an herbivore’s teeth are its most important tool, and anyone who has used sandpaper knows that grains of sand can wear down hard surfaces. Plants worldwide may be wielding a sandy shield to avoid becoming a meal, say the researchers, who add that the armor could still have other uses, like protection against sandstorms.